ADA4255ACPZ-R7 datasheet(32/64 Pages) AD

32 / 64 page

Data Sheet

ADA4255

THEORY OF OPERATION

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Rev. 0 | 32 of 64

In Figure 94, five distinct CS pulses can be seen. The first CS

pulse writes 0x03 to the GPIO_DIR register to configure GPIO0 and

GPIO1 as outputs. The second CS pulse writes 0x03 to SCS to

configure GPIO0 and GPIO1 for SCS mode. The third CS pulse is

replicated on GPIO0 and communicates with the first slave device,

an ADC in this case. The fourth CS pulse is replicated on GPIO1

and communicates with the second slave device, a DAC in this

case. The fifth CS pulse communicates with the ADA4255 itself.

This pattern of communication continues in order of ADC, DAC, and

ADA4255 until SCS is changed.

Figure 94. SCS Configuration and Operation with Two Slave Devices

GAIN ERROR CALIBRATION

The ADA4255 includes measured gain errors for all 32 gain com-

binations, readable from the on-chip, read only memory (ROM).

These errors are measured at 25°C and are stored in Register

0x10 through Register 0x27 at the time of production. Using this

technology improves gain accuracy by a factor of 5, improving

system accuracy and reducing additional calibration requirements.

Each register contains five bits. MSB represents the polarity of the

error, with a setting of 1 indicating a negative polarity and a setting

of 0 indicating a positive polarity. The remaining four bits contain

the magnitude based on a LSB of 100 ppm for GAIN_CAL1 through

GAIN_CAL12 and 50 ppm for GAIN_CAL13 through GAIN_CAL24.

GAIN_CAL1 through GAIN_CAL12 directly provide the measured

gain errors of all 12 gain values with the scaling gain set to 1 V/V.

GAIN_CAL13 through GAIN_CAL24 provide additional gain error

incurred when using other scalar gains. This is tabulated in Table 7.

Table 7. Gain Calibration Register Contents1

Name

G[3:0]

Contents

0x10

GAIN_CAL1

0b0000

Gain error for G = 1/16 V/V × 1 V/V

0x11

GAIN_CAL2

0b0001

Gain error for G = 1/8 V/V × 1 V/V

0x12

GAIN_CAL3

0b0010

Gain error for G = 1/4 V/V × 1 V/V

0x13

GAIN_CAL4

0b0011

Gain error for G = 1/2 V/V × 1 V/V

0x14

GAIN_CAL5

0b0100

Gain error for G = 1 V/V × 1 V/V

0x15

GAIN_CAL6

0b0101

Gain error for G = 2 V/V × 1 V/V

0x16

GAIN_CAL7

0b0110

Gain error for G = 4 V/V × 1 V/V

0x17

GAIN_CAL8

0b0111

Gain error for G = 8 V/V × 1 V/V

0x18

GAIN_CAL9

0b1000

Gain error for G = 16 V/V × 1 V/V

0x19

GAIN_CAL10

0b1001

Gain error for G = 32 V/V × 1 V/V

0x1A

GAIN_CAL11

0b1010

Gain error for G = 64 V/V × 1 V/V

0x1B

GAIN_CAL12

0b1011

Gain error for G = 128 V/V × 1 V/V

0x1C

GAIN_CAL13

0b000x

Additional gain error for G = 1/16 V/V × 1.375 V/V or G = 1/8 V/V × 1.375 V/V

0x1D

GAIN_CAL14

0b001x

Additional gain error for G = 1/4 V/V × 1.375 V/V or G = 1/2 V/V × 1.375 V/V

0x1E

GAIN_CAL15

0b010x

Additional gain error for G = 1 V/V × 1.375 V/V or G = 2 V/V × 1.375 V/V

0x1F

GAIN_CAL16

0b011x

Additional gain error for G = 4 V/V × 1.375 V/V or G = 8 V/V × 1.375 V/V

0x20

GAIN_CAL17

0b100x

Additional gain error for G = 16 V/V × 1.375 V/V or G = 32 V/V × 1.375 V/V

0x21

GAIN_CAL18

0b101x

Additional gain error for G = 64 V/V × 1.375 V/V or G = 128 V/V × 1.375 V/V

0x22

GAIN_CAL19

0b000x

Additional gain error for G = 1/16 V/V × 1.25 V/V or G = 1/8 V/V × 1.25 V/V

0x23

GAIN_CAL20

0b001x

Additional gain error for G = 1/4 V/V × 1.25 V/V or G = 1/2 V/V × 1.25 V/V

0x24

GAIN_CAL21

0b010x

Additional gain error for G = 1 V/V × 1.25 V/V or G = 2 V/V × 1.25 V/V

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